Homeland Security chief says family separations at U.S. border are down

McAleenan was speaking Thursday before the House Oversight Committee investigating border problems. His testimony comes amid a growing outcry over the treatment of migrants at the border, an internal investigation into Border Patrol agents who posted crude and mocking posts in a secret Facebook group and the move this week to effectively end asylum on the U.S.-Mexico border.

Lawmakers mostly questioned McAleenan about the policy that led to the separation of more than 2,700 children from parents last year. A watchdog reporter later found thousands more may have been separated. Democrats and Republicans on the committee also traded barbs over emergency border funding and the moment the massive numbers of border crossings became a crisis.

“As I have testified and warned publicly, dozens of times this year and last, we are facing an unprecedented crisis at the border,” McAleenan told the committee.

READ MORE: Trump says he will not return to policy of family separation

U.S. Customs and Border Protection officials have encountered more than 800,000 migrants crossing the border from Mexico. Over 450,000 were families.

“Combined, that means over 300,000 children have entered our custody since Oct. 1,” he said.

House Oversight Committee Chairman Elijah Cummings, a Maryland Democrat, said McAleenan was an architect of the family separations. McAleenan wrongly called reports of filthy, overcrowded border facilities “unsubstantiated,” Cummings said.

“The administration wants to blame Democrats for this crisis, but it is the Trump administration’s own policies that are causing these problems,” Cummings said.

WATCH: Democrats continue to push for hearings on border as Pence blasts comparisons to concentration camps

Rep. Alexandria Ocasio-Cortez, a New York Democrat, questioned McAleenan about the Border Patrol Facebook posts, some of which included graphic, doctored images of her.

Ocasio-Cortez asked whether the agents were still on duty and wondered whether the family separation policy had contributed to a “dehumanizing culture.”

McAleenan said some had been placed on administrative duty but didn’t elaborate.

READ MORE: Judge may order Trump admin to reunite more migrant families separated at Mexico border

“We do not have a dehumanizing culture,” McAleenan responded.

Lawmakers didn’t question McAleenan on the new asylum rules. But the new policy is by far the biggest change to how the U.S. handles immigrants. Under the new rules, anyone who comes to the U.S.-Mexico border through another country would not be eligible for asylum. They could affect tens of thousands of people who cross the border each month. There are thousands more on waiting lists at ports of entry who will now likely be denied asylum.

The new rules come into play during an initial asylum screening that happens after a migrant is first encountered by Border Patrol, so they won’t make an immediate dent in overcrowding at border facilities. The rules also must survive a legal challenge.

WATCH: DHS report says U.S. migrant detention facilities are “ticking time bomb”

Mark Morgan, the acting head of U.S. Customs and Border Protection, said in an interview with NPR on Thursday that the policy would be rolled out starting with a pilot program in the Rio Grande Valley. Morgan’s agency is responsible for initial encounters with migrants, but the asylum officers who will decide whether a migrant is eligible for protections work under U.S. Citizenship and Immigration Services.

The number of border crossings dropped last month amid hot weather and a crackdown by Mexico on migrants to its southern border.

McAleenan said facilities are less crowded, especially for children who are only supposed to be held in border holding stations for 72 hours. Delays along the entire immigration system have forced migrants to wait in crowded border facilities not meant to hold people for more than a few days.